In the illustration above, note that the battery slides under the battery clip, not on top. Be sure the plus (+) side is facing up. Incorrect insertion will burn out the circuit or break the solder connection.
The cover should only be finger tight and snug, so as to remain waterproof. Please do not use pliers or other tools to tighten the cap onto the transmitter. Over-tightening will damage the o-ring. Obvious signs of abuse such as plier teeth marks will void the warranty.